The invention relates to electrical apparatus and more particularly to an adjustable interlock for safe operation of microwave ovens.
The source of microwave energy utilized in microwave ovens is the magnetron which is now well known in the art. Such magnetron generators provide for radiation of energy within an enclosure to heat any food article disposed therein. Magnetron energy generators conventionally operate from regular line sources of low frequency and low voltage which is stepped up to DC rectified voltages of 4,000 to 6,000 volts. To provide for safe operation, interlock switches have evolved in the prior art to interrupt the line power and prevent radiation of energy except when the door to the enclosure is closed. Such interlock switches prevent serious damage to the expensive equipment and are intended, with associated electrical circuitry, to substantially reduce any hazards associated with the high voltage supplies. A concern about such devices has been the possibility of radiation leakage which might result in injury to the operator. Because of this concern, the Department of Health, Education and Welfare, through the Bureau of Radiological Health (BRH), has promulgated a series of regulations specifying minimum safety precautions for microwave ovens manufactured or sold in the United States.
All such ovens are required to have a minimum of two safety interlocks. At least one safety interlock must be concealed, and the concealed interlock must not be operable by any part of the human body, any object with a straight insertable length of ten (10) centimeters, or a test magnet held in place on the oven by gravity or its own attraction.
It is further required that any visible actuating member of the concealed safety interlock must not be intended for removal by conventional tools without full or partial disassembly of the door. It must also have an apparent useful purpose and function other than interlock actuation unless access to the interlock is prevented when the door is open. Finally it is required that a means of monitoring at least one of the safety interlocks be provided to cause the oven to become inoperable if the safety interlock should fail.
Since the interlock switches are required to open and close each time the apparatus is operated, such devices must be completely reliable and adequately disable the electrical circuits at any time that a potentially hazardous condition arises. Mass production techniques compound the difficulty in attaining a truly reliable safety interlock. Assembly line manufacturing makes it necessary that the interlock be economical to produce, easy to install, convenient to adjust and consistently reliable from oven to oven. But most important, the adjustment must be precise. The accuracy of the setting cannot be compromised for ease of production.